Method for assembling a two substrate parallel optical sub-assembly

ABSTRACT

There is provided an optical assembly and a method for assembling components of the optical assembly, the method comprising: providing a structure for guiding light; providing a plurality of optical fibers embedded in a fixed arrangement in the structure, the optical fibers for coupling the light from a coupling surface the structure; abutting a first package against the coupling surface, such that each one of multiple elements comprised in the first package is substantially aligned with each one of a first group of optical fibers in the plurality of optical fibers; and abutting a second package against the coupling surface, adjacent to the first package, and such that: the first and the second package are spaced apart by a gap; and each one of multiple elements comprised in the second package is substantially aligned with each one of a second group of optical fibers in the plurality of optical fibers, the gap providing a tolerance in a position of any one of: each one of the elements in the packages; the packages with respect to each other; and each one of the packages with respect to the structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 11/862,594 filed on Sep. 27, 2007, the contents of which are herebyincorporated by reference. The present application also relates to U.S.Pat. No. 7,178,235 granted Feb. 20, 2007 entitled METHOD OFMANUFACTURING AN OPTOELECTRONIC PACKAGE and U.S. Pat. No. 7,197,224granted Mar. 27, 2007 entitled OPTICAL FERRULE, the specifications ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

This description pertains to the field of precision alignment ofmultiple devices. More precisely, it relates to the field of opticalalignment of three or more elements.

BACKGROUND OF THE PRESENT INVENTION

There has been much work devoted to the alignment of lasers (orphotodetectors) with optical fibers to provide for the maximum amount ofcoupling and subsequent transmission of light along an optical fiber.Most products are based on a single laser aligned to a single opticalfiber—an example is the SFP optical transceiver, with a well alignedtransmitter module and a well aligned receiver module; each with asingle optical fiber coupling in an LC connector housing.

However, due to ever growing demands for bandwidth in smaller overallvolumes of space (known as a higher bandwidth-density) there has been anincreasing trend towards parallel optical modules where multiple lasersare aligned to multiple optical fibers in a single module—an example ofthis is the SNAP-12 parallel optical transceiver with 12 opticalchannels in an area roughly 1-cm×1-cm. Both single and multiple opticalchannel modules require well positioned and well tolerancedsub-components and holders—such as described by Gallup, et al., U.S.Pat. No. 6,955,480 granted Oct. 18^(th), 2005 and Kanazawa, et al., U.S.Pat. No. 6,179,483 granted Jan. 30^(th), 2001. Furthermore, they areusually aligned while actively monitoring the optical power levels, toor from the optical fiber, to ensure the highest possible coupling(lowest insertion loss)—this is especially true for modules with longlink distances (>1-km) that are based on single mode optical fiber, butalso is needed for modules with shorter link distances (<300-m) that arebased on multimode optical fiber.

The principle behind the alignment of the parallel optical module hasbeen to use several levels of aligned module or components starting withphoto-lithographically defined patterned arrays of lasers (orphotodetectors). These arrays can be made with extremely highresolution, typically better than 1-micron tolerance for 12 lasers on a250-micron pitch. These VCSEL arrays of lasers are produced as singlechips roughly 3-mm×0.3-mm×0.15-mm with 12 lasers in a row. The alignmentbetween the laser array and the optical fibers requires a morecomplicated set of parallel holders and relay optics—such as a patternedmicrolens array and an MT-style optical ferrule—but requires the samealignment methodology as the single laser module—just done on both endsof the array at the same time. The difficulty here is that alignment istime consuming, requires additional components (like relay microlenseswith dowel pin alignment post), requires the lasers to be powered-on foractive alignment, and requires precision pick-and-place techniques toplace the VCSEL chips.

A further complication to this alignment strategy for parallel opticalmodules, has been an increasing demand to include both out-going andin-coming optical signals within the same single, small form—factormodule. This requires that both the laser arrays (VCSELs) andphotodetector arrays (PDs) be placed along side each other where asingle high-density optical connector (such as the MT ferrule) is usedto maintain the bandwidth-density advantage of the module. A fewexamples of modules which have both out-going and in-coming optical datasignals are the POP-4 transceiver and the QSFP transceiver. This type ofalignment requires three independent parts to be aligned with respect toeach other where typically the VCSEL and PD arrays are aligned together,such that they are pitched on 250-micron centers and in co-linearposition of their active areas (and not necessarily the sides of thechips). This further compounds the earlier active alignment issues asdescribe above and increases the alignment time, the set-up time and theaccuracy of the equipment required.

SUMMARY

The present description provides a method and apparatus for thealignment of 2 (or more) optoelectronic devices with a single structurecontaining multiple optical waveguides or optical fibers.

This description relates to the optical coupling of light that requiresmultiple optical coupling operations to micron (or sub-micron) tolerancelevels to produce an optical sub-assembly comprised of both input andoutput electrical signals and input and output optical signals forbi-directional optical components.

This description provides concepts that are directed towards themanufacturability of volume quantities of bi-directional opticalsub-assemblies. This assembly provides for a low-profile, robustsub-component that can be used in a variety of optical modules.Furthermore, the methods described to construct the sub-component allowfor low-cost manufacturing.

The description provides a means for bi-directional optical datacommunications using at least 2 optical channels and consists of atleast one light emitting device on a chip that has been mounted on anelectrical interconnecting substrate, at least one light detectingdevice on a chip that has been mounted on an electrical interconnectingsubstrate, and an optical guiding structure that holds at least 2optical channels, where at least one optical channel is for outputoptical signals and the other is for input optical signals. Structuresthat contain multiple pathways for light, such as a polymer waveguidesor a structure that contains a lens array can also be envisioned.

Many of the optical alignment techniques used to align an optoelectronicdevice on a substrate to an optical guiding structure are described inboth the OPTICAL FERRULE patent and U.S. Pat. No. 7,178,235 entitledMETHOD OF MANUFACTURING AN OPTOELECTRONIC PACKAGE. However, severalnovel optical alignment aspects are involved when aligning three (ormore) independent objects, especially when each component involves morethan 1 optical channel, without the use of expensive pick-and-placeequipment. Prior art, such as the method and assemblies used in thealignment of bi-directional, parallel POP-4 transceiver modules, asshown in FIG. 01, are based on first aligning each optoelectronic chipto a common carrier and also to each other. The next step is to alignthe optical guiding structure, in this case the microlens array, to thepair of optoelectronic chips.

In this description, there is still basically the same number of opticalalignment steps, except that they are performed in a different sequenceand done on different, specially designed, sub-components. Eachoptoelectronic chip, the emitter chip and the detector chip, is alignedto the optical guiding structure independently from the other. Once allfixed together, the final assembly can then be mounted on a commoncarrier (typically a printed circuit board) and connected electrically.In this way, the very precise mechanical placement of very smalldevices, such as the optoelectronic chips, can be eliminated and thusthe cost can be reduced as well as the time required.

Another aspect of this description is that the vertical spacing of theactive area of the emitter array to the optical interface of the opticalguiding structure can be different from the vertical distance betweenthe active area of the detector array and the optical interface of thesame optical guiding structure.

Yet another aspect of this description is that the electricalconnections (such as wirebonds) between the optoelectronic arrayeddevices and their respective substrates can tolerate a large variationin ideal position as does the electrical connection between thecompleted optical assembly and the common carrier. The type of opticalalignments proposed combined with the positional flexibility of theelectrical connections to the conductive trace lines eliminate the needfor precision pick-and-place equipment and speed up assembly time.

Accordingly, the present description provides an optical assemblycomprising: a structure for guiding light; a plurality of optical fibersembedded in a fixed arrangement in the structure, each of the opticalfibers having a coupling surface for coupling light from a side surfaceof the structure; and a plurality of packages abutted against thecoupling surface, adjacent to each other and spaced apart to form atleast one gap, each one of the packages comprising an element, theelement being substantially aligned with the coupling surface of one ofthe optical fibers, the gap providing a tolerance in a position of atleast one of: the element in the packages; the packages with respect toeach other; and each one of the packages with respect to the structure.

Accordingly, the present description also provides a method forassembling components of an optical assembly, the method comprising:providing a structure for guiding light; providing a plurality ofoptical fibers embedded in a fixed arrangement in the structure, theoptical fibers for coupling the light from a coupling surface thestructure; abutting a first package against the coupling surface, suchthat each one of multiple elements comprised in the first package issubstantially aligned with each one of a first group of optical fibersin the plurality of optical fibers; and abutting a second packageagainst the coupling surface, adjacent to the first package, and suchthat: the first and the second package are spaced apart by a gap; andeach one of multiple elements comprised in the second package issubstantially aligned with each one of a second group of optical fibersin the plurality of optical fibers, the gap providing a tolerance in aposition of any one of: each one of the elements in the packages; thepackages with respect to each other; and each one of the packages withrespect to the structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 01 is an exploded view of a transceiver assembly for abi-directional parallel optical module in accordance with the prior art;

FIG. 02 is a perspective view of an MT-style parallel optical fiberferrule in accordance with the prior art;

FIG. 03 is a perspective view of an optical ferrule in accordance withthe prior art;

FIG. 04 a is a perspective view of a two-substrate parallel opticalsub-assembly in accordance with an embodiment described herein;

FIG. 04 b is an enlarged view of the two-substrate parallel opticalsub-assembly of FIG. 04 a showing the optoelectronic chips and theoptical coupling mechanism;

FIG. 05 a is a top view of the alumina substrate of FIG. 04 a and FIG.04 b, for a light emitting chip, with the maximum allowable positionaltolerance of the chip on the substrate being indicated;

FIG. 05 b is a top view of the alumina substrate of FIG. 04 a, and FIG.04 b, for a light detecting chip, with the maximum allowable positionaltolerance of the chip on the substrate being indicated;

FIG. 06 is a top view of an ideal position of the light emitting chipwith respect to the light detecting chip of FIG. 05 a and FIG. 05 b, ontheir respective alumina substrates;

FIG. 07 a is a top view of the two-substrate parallel opticalsub-assembly of FIG. 04 a and FIG. 04 b, with the substrates and theoptical ferrule being perfectly aligned and positioned;

FIG. 07 b is a top view of the two-substrate parallel opticalsub-assembly of FIG. 04 a and FIG. 04 b, with the substrates and theoptical ferrule being aligned but not perfectly positioned;

FIG. 08 is a top view of the two-substrate parallel optical sub-assemblyof FIG. 04 a and FIG. 04 b, with the substrates having an alternativeshape;

FIG. 09 is a front cross-sectional view of the two-substrate paralleloptical sub-assembly of FIG. 04 a and FIG. 04 b, with the verticalheight differences between the two substrates and the optical ferrulebeing shown;

FIG. 10 is a perspective view of the two-substrate parallel opticalsub-assembly of FIG. 04 a and FIG. 04 b, in an unassembled stage whereinthe light emitting apertures are to be aligned with the ends of theoptical fibers of the optical ferrule; and

FIG. 11 is a perspective view of the two-substrate parallel opticalsub-assembly of FIG. 04 a and FIG. 04 b, in an unassembled stage whereinthe light detecting apertures are to be aligned with the ends of theoptical fibers of the optical ferrule.

DETAILED DESCRIPTION

In one embodiment, a two substrate parallel optical sub-assembly isproposed that incorporates a laser array optoelectronic chip, aphotodetector array optoelectronic chip and a means for couplingmultiple light channels to and from each chip through a coupling side ofthe structure.

The two substrate parallel optical sub-assembly uses a single opticalguiding structure composed of an arrangement of multiple, fixed,well-aligned or parallel optical guiding channels (or optical fibers)which may be embedded in the structure. The arrangement of the opticalfibers in the structure may vary.

The optical guiding structure typically has a single “external” opticalinterface—like the multi-terminal (MT) style of parallel opticalconnector as shown in the prior-art example in FIG. 02—to maintain ahigh bandwidth-density ratio.

The optical guiding structure that is used herein is based on the priorart patent called an “OPTICAL FERRULE”. Referring to FIG. 03, the priorart optical ferrule is composed of an MT-style optical connector [01]with two dowel pins [03] (only shown in FIG. 04 a), a short opticalfiber ribbon section [05], and silicon v-groove structure [07]. Thestructure 07 has a coupling side from which light is coupled. Thestructure also holds the beveled tips (or ends) [21] of the embeddedoptical fibers in place along the coupling side and such that a couplingsurface of each of the optical fibers is substantially near a beveledside of the structure.

A precision end-couple ferrule member can be provided at a connector endopposite from the beveled side of the structure, for guiding acomplementary ferrule member to end-couple fiber-to-fiber the pluralityof optical fibers at the connector end, wherein the substantially flatcoupling side is also near the connector end.

FIG. 04 a shows an example of a two-substrate parallel opticalsub-assembly, herein simply referred to as an optical assembly. Theoptical assembly has an optical guiding structure having an opticalferrule such as shown in FIG. 03. Each optoelectronic device, the VCSELarray [09] and the photodetector array [11], are attached to their ownrespective alumina substrates [13] and [15], and wirebonded to goldtrace line electrical conductors [17] and [19].

Referring to FIG. 04 b, in this embodiment, the optical ferrule used has12 aligned, parallel optical fibers [05] that have 45-degree beveled endtips [21] that are all co-linear and on a pitch of 0.25-mm, a close-upview of the tips of the optical fibers is shown in FIG. 04 b.

Referring to both FIGS. 4 a and 4 b, the other end of the opticalferrule is compatible with a single multi-terminal optical connector[01] called an MT ferrule. In this case, only 8 of the 12 opticalchannels are used—there are 4 transmitter channels (optical fibers), 4unused channels (optical fibers) in the middle, and 4 receiver channels(optical fibers). The unused set of optical fibers is used as aseparation (also referred to as a gap having a gap length) [23] betweenthe transmitter and receiver groups of optical fibers to provide forsome alignment clearances for the 2 alumina substrates. The 2 groups ofoptical fibers within the optical guiding structure are fixed in-place,with a fixed separation [23] defining a gap length.

Each alumina substrate has an optoelectronie chip fixed to its surface—alight emitting chip, the VCSEL array [09] and a light detecting chip,the photodetecting chip [11]. However, other combinations ofemitter-emitter or detector-detector chips, especially for differentwavelengths, can also be envisioned. The substrates are be designed sothat they can be individually handled and not obstruct each other duringoptical alignment. In this particular embodiment, the alumina substrateshave been designed to be long and narrow with the optoelectronic chipsplaced near either edge of each substrate.

The allowable positional and rotational tolerance of the optoelectronicchip on the substrate depends on the overall sizes and shapes of all thesub-components of the assembly. In this particular embodiment, thesubstrates are mirror images of each other, as in FIG. 05 a and FIG. 05b. The nominal positional and rotational tolerance of eachoptoelectronic chip on their respective substrate is indicated in FIG.06 by the dashed ovals [25] and [27] placed around each chip; the VCSELchip [09] and a photodetecting chip [11], respectively.

In this particular case, one substrate contains a 1×4 VCSEL laser arraythat is 1-mm×0.3-mm in footprint and is placed near one edge of itsrespective alumina substrate and is wirebonded to the gold traces(wirebonds are not shown). The other substrate contains a 1×4 PD arraythat is 1-mm×0.3-mm in area and is placed near one edge of itsrespective alumina substrate and is wirebonded to the gold traces(wirebonds are not shown). Both optoelectronic chips [9] and [11] areplaced on the edges of their respective alumina substrates [13] and [15]such that they are adjacent to one another and form a mirror-imagepattern.

Still as shown in FIG. 06, the centers of the active areas of the VCSELchip [9] and the photodetector chip [11] lie along the dashed horizontalline [29]—it is noted that aligning the sides of the optoelectronicchips may not in fact align the centers of the active areas. At aminimum, most dice cuts along semiconductor chips have tolerances ofmore than +/−25-microns, so the sides of the chips may not be sufficientto align the active areas properly with respect to one another.

A second alignment consideration is that of the pitch between thedevices. The 12 vertical dashed lines [31] indicate a pitch of 0.25-mmbetween the centers of adjacent active areas for both chips.—The dashedlines [31] continue in the space (also referred to as a gap) section[23] between the two independent substrates, as shown in FIG. 06. Thepitch is also referred to as a distance between the centers of theactive areas along the dashed horizontal line [29]. Hence, the gaplength along the line [29] is greater than the distance between thecenters of the active areas along the line 29].

As an example, given an optical ferrule that is 7-mm×7-mm in area, wherethe 12 optical fibers are parallel and vertically centered in theoptical ferrule with a pitch of 0.25-mm, the gap between the 2 outergroups of 4 optical fibers is 1.125-mm. Given that the length (L) ofeach alumina substrate is 10-mm, it can be calculated that thepositional tolerance of both the VCSEL [9] and PD arrays [11] withrespect to their ideal positions is roughly +/−0.3-mm in both x and yand have a rotational tolerance of +/−2-degrees.

Therefore, when the optoelectronic chips are well-aligned to the opticalfibers [05] in the v-groove structure [07] of the optical ferrule, andthey have also been well aligned to their substrate [13] or [15], theorientation as shown in FIG. 07 a is obtained.

However, if the optoelectronic chips are placed with low positional androtational accuracy on their substrate (but within the dashed ovalboundaries [25] and [27] shown in FIG. 06), once the active areas ofeach chip [9] or [11] are aligned to the optical fibers of the opticalferrule, the orientation shown in FIG. 07 b is obtained.

The worse case scenario is that the alumina substrates [13] and [15]will only just touch at one corner [33]. This relatively large placementtolerance therefore allows the optoelectronic devices [9] and [11] to beplaced without the use of high-precision pick-and-place equipment andreduces the cost and time of the assembly.

Other geometries for alumina substrates [13] and [15] exist. There aretrade-offs between their manufacturability and their ease of alignmenthowever. A specific example of another geometry would be to usesubstrates with protruding vertices [35], as shown in FIG. 08, where theoptoelectronic chips would be placed near the vertex of their substrate[13] or [15]. This would lead to a greater tolerance to positional androtational alignment of the two substrates (since the substrates wouldbe much less likely to interfere with one another). Such substrategeometry could however be more difficult to manufacture. Other examplesof substrate shapes and related trade-offs are also possible.

Referring to FIG. 09, in addition to the positional and rotationalplacement of the optoelectronic chips [09] and [11] on their respectivealumina substrates [13] and [15], the vertical height above theoptoelectronic chip can be calibrated using a precision spacer (alsoreferred to as a spacing device) [39] or [41] fixed to any of thesubstrates [13] or [15].

Different heights of emitter and detector optoelectronic chips can beaccommodated by using different thickness for the spacers. A spacer canbe made of glass or any other low-expansion precision cut material. Thespacer can also accommodate differing optimal divergence conditions orlensing system requirements.

For example, FIG. 09 shows a front side view of the two substrateoptical sub-assembly of FIG. 04 a and FIG. 04 b in a highly magnifiedbut proportional view of the space (or gap) [23] and the two adjacentwirebonded [37] optoelectronic chips [9] and [11]. Assuming a 1×4 VCSELarray chip [09] which is 200-microns thick and requires a distance [44]of 132.5-microns between the laser aperture (or the active area of thelasing element on the chip [9]) and the centre of the optical fiber, aprecision spacer of 280-microns [39] is needed.

With a 1×4 photodetector array [11] which is 150-microns thick andrequires a distance [46] of 102.5-microns between the active area of thedetector element and the centre of the optical fiber, a precision spacerof 190-microns [41] is needed.

Although a small vertical height difference [43] between the twosubstrates [13] and [15] may be incurred, these small differences can behandled in a variety of ways to maintain electrical and mechanicalconnections, such as different substrate thicknesses or the use ofdifferent amounts of epoxy and/or longer or shorter wirebonds orelectrical connections between the chips and their substrates [37].

Alignment Procedure:

Where the optical guiding structure has the optical ferrule as describedhereinabove, and when the useful channels of the optical ferrule are bethe left-most 4 optical fibers and the right-most 4 optical fibers, withthe middle 4 optical fibers being left unused, the alignment of thethree parts (the optical ferrule with the two packages each comprisingan optoelectronic device, a substrate and an optional spacer) are asfollows:

The first alumina substrate [13] carrying a wirebonded 1×4 VCSEL arraychip [9] as well as a vertical spacer [39] is aligned using a visionsystem so that the centers of each active area of each VCSEL arecentered with the centers of the 4 optical fiber cores on one side ofthe body of the optical ferrule, as shown in FIG. 10.

The above alignment is done by holding the first alumina substrate [13]fixed in place while manipulating the body of the optical ferrule in x,y and rotation, as indicated by the dashed arrows [45], and whileresting on the vertical spacer [39]. Resting on the spacer restricts theoverall movement of the optical ferrule to only about 3 degrees ofmotion during an alignment which is performed by manipulating theoptical ferrule using, for example, a vacuum chuck.

The first substrate [13] is then epoxy cured in place to the opticalferrule, as indicated by the black material [47] in FIG. 11.

Still referring to FIG. 11, the second alumina substrate [15] carrying awirebonded 1×4 Photodetector array chip [11] as well as a verticalspacer [41] is then held fixed in place while the assembly of theoptical ferrule with the first substrate [13] is manipulated in x, y androtation, as indicated by the dashed arrows [49], and while resting onthe vertical spacer [41] of the second substrate [15].

Once positioned and aligned over the second substrate [15], the opticalferrule can be held in place using a vacuum suction holder, for example,to allow the positioning of the centers of each of the fibers (alsoreferred to as the centers of the coupling surfaces of the fibers) inthe second group of 4 optical fibers over each one of the active areasof the elements in the array of elements of the photodetector chip [15].A vision system is also used to perform the alignment. The vision systemcan be any system permitting a visual, un-powered alignment. Hence,there is no need to use passive mechanical stops or location borders.Such a system also avoids using a “blind” search for a maximal opticalpower to perform the alignment.

The second substrate [15] is then attached or epoxy cured in place tothe body of the optical ferrule along side the first substrate [13]resulting in the assembly as illustrated in FIG. 04 a (without the epoxybeing shown). Other types or combinations of attaching device can bechosen depending on the attachment reliability level needed for aparticular assembly. For example, such attaching devices can also beultrasonic bonding, thermal bonding, or a mechanical clamp.

Once the second substrate [15] is attached to the body of the opticalferrule along side the first substrate [13], a defined gap [23] betweenthe two substrates exists but its exact shape is determined by theinitial positioning of the VCSEL and Photodetector chips on theirrespective substrates.

Other optical guiding structures can be envisioned for this geometryincluding lens arrays and parts made from polymer waveguiding materials.The basic premise is to align two very small parts to the same opticalguiding structure—given that each part is on its own, larger, sub-mountand there is a provisioned amount of positional tolerance in theassembly to accommodate the independent movement of each sub-mount. Thisis in contrast to aligning the very small parts to each other and thenaligning to an optical guiding structure.

The skilled person in the art will appreciate that in the abovedescription, the optoelectronic chips [9] and [11], together with theirrespective substrate [13] and [15], represent packages having an arrayof elements. The elements can be any type semiconductor type deviceshaving light emitting, light detecting or light guiding (such asmicrolenses) capabilities. Each of the elements is further characterizedas having an active area to be aligned with the ends of the opticalfibers in the structure when abutting the packages on the structure.

The above description refers to an optical assembly having twosubstrates, or two packages each comprising a substrate with elementsbeing on the substrate. It is understood that an assembly having morethan two packages can be assembled without departing from the scope ofthe description. The substrates can also be of any other material thatalumina which is suitable for the placement of the elements desired,such as Silicon or Germanium alloys for example.

Moreover, the packages may be abutted against the structure in othermanners as described, with or without the use of a spacing device toprovide for a space between the elements of the packages and the opticalfibers in the structure.

1. A method for assembling components of an optical assembly, the method comprising: providing a structure for guiding light, the structure having grooves on a coupling side; providing a plurality of optical fibers, each being embedded in a corresponding One of said grooves and having a coupling surface; abutting a first package comprising a plurality of first elements against the coupling side, such that each one of the plurality fo first elements comprised in the first package is substantially aligned with a corresponding one of a first group of optical fibers in the plurality of optical fibers; attaching the first package to the structure: abutting a second package comprising a plurality of secon elements against the coupling side, adjacent to the first package, and such that: the first and the second package are spaced apart by a gap; and each one of the plurality of second elements comprised in the second package is substantially aligned with a corresponding one of a second group of optical fibers in the plurality of optical fibers, the gap allowing a position of the plurality of second elements in the second package to be independent of a position of the plurality of first elements in the first package; and attaching the second package to the structure.
 2. The method as in claim 1, wherein the abutting of the first package and the abutting of the second package comprises using a vision system.
 3. The method as in claim 1, wherein the abutting of the first package comprises aligning a center of an active area of each one of the plurality of the first elements with a center of the corresponding one of the first group of optical fibers andd the abutting of the second package comprises aligning a center of an active area of each one of the plurality of the second elements with a center of the corresponding one of the second group of optical fibers.
 4. The method as in claim 1, wherein the abutting of the first package comprises providing a first spacing device between the coupling side and the first package.
 5. The method as in claim 4, wherein the abutting of the first package comprises: holding the first package and the first spacing device in a fixed position; moving the structure until the elements of the first package are aligned with the coupling surface of the optical fibers of the first group in a one-t-oone manner, the moving and the holding being performed simultaneously; and resting on the first spacing device while performing the moving.
 6. The method as in claim 5, wherein the moving of the structure comprises using a vacuuming device.
 7. The method as in claim 5, wherein the abutting of the second package comprises providing a second spacing between the coupling side and the second package.
 8. The method as in claim 7, wherein the abutting of the second package comprises: holding the second package and the second spacing device in a fixed position; moving the structure until the elements of the second package are aligned with the coupling surface of the optical fibers in the second group of optical fibers in a one-to-one manner, the moving and the holding being performed simultaneously; and resting on the second spacing device while performing the moving.
 9. The method as in claim 8, wherein the moving of the structure until the elements of the second package are aligned comprises using a vacuuming device. 